The present invention relates generally to a method and device for media access layer feedback in a packet data communication system and, more particularly, to a method and device for providing acknowledgments and time slot assignments using a new packet channel feedback field.
Current North American Time Division Multiple Access (TDMA) systems support voice services and circuit data services at a rate limited to 9.6 kb/s. High rate packet data services are desirable for short bursty transactions and other applications, such as world wide web/internet access, electronic mail and file transfer. Accordingly, the Telecommunications Industry Association (TIA) has adopted flexible, high performance Medium Access Control (MAC) and Radio Resource Management procedures for high rate packet data services over IS-136 TDMA channels. The characteristics of these procedures, such as a 30 kHz channel bandwidth, symbol rate and TDMA format (6 time slots every 40 ms), are in compliance with the IS-136 standard to provide compatibility with existing mobile units and in order to minimize impact on existing infrastructure.
The standards for the packet data MAC and physical layer have been designed to support higher data rates through the use of higher modulation schemes. The standard is designed to permit dynamic adaptation of the modulation scheme based on measured carrier to interference ratios (C/Is). Supported modulation schemes include coherent 8 phase shift keying (PSK) and π/4 Differential Quadrature Phase Shift Keying (DQPSK).
As set forth in the standards, a packet data channel (PDCH) is provided consisting of six logical channels. In particular, the PDCH consists of a packet broadcast channel for indicating generic system configuration related information, a packet paging channel dedicated to delivering pages, a downlink packet payload channel for delivering data generated by Logical Link Control (LLC) and General Packet Radio Services (GPRS) Mobility Management, Packet Channel Feedback (PCF) for support of random access and reserved access on the uplink, uplink packet random access channel used by mobile stations to request packet data access to the system and reverse packet payload channel for delivering data generated by the LLC and GPRS Mobility Management.
Unfortunately, the PDCH has a limited 30 kHz channel bandwidth which thus necessarily restricts the data rates that can be supported. Accordingly, there is a need in the art for methods and systems which increase the data rates possible over the PDCH and are in compliance with the standards for IS-136 time division multiple access systems.
The PDCH uses 30 kHz radio frequency channels and the time slotted structure specified in IS-136. Each 40 ms frame on a 30 kHz RF channel consists of 6 time slots (3 time slot pairs), numbered 1 to 6. One or more time slot pairs may be allocated to a PDCH. The remaining time slot pairs may be allocated to a digital control channel (DCCH) and/or digital traffic channel (DTC). A PDCH may be full rate, double rate or triple rate depending on whether 1, 2 or 3 time slot pairs are allocated to the channel within each 40 ms frame.
A multi-rate PDCH operates on a single channel frequency and consists of primary and secondary phases. In this context, a phase corresponds to a full rate portion of a multi-rate PDCH. The primary phase always corresponds to a full rate channel and is the only full rate channel that contains logical paging and broadcast channels on the downlink. Nominal paging time slots are determined using a standard hashing algorithm that relies on mobile station (subscriber) identity. Sleep mode similar to the IS-136 DCCH is defined for mobile stations in order to improve standby time.
In addition, the shared channel feedback (SCF) procedures and fields as specified in IS-136 DCCH are not well-suited for long packet data transactions and do not facilitate flexible sharing of resources among users.
Accordingly, there is a need in the art for a method and device for handling contention in a better and more flexible manner and for assigning time slots in a more flexible manner.